Cultured cell systems are being used to investigate aspects of nervous system development and regulation of function. Specifically, (1) the induction, mediated by muscle conditioned medium, of choline acetyltransferase activity in spinal cord cell cultures was found to require a high molecular weight factor or factors which could also be obtained from an homogenate of embryonic muscle. (2) Cerebellum cells from newborn rats were found to adhere rapidly and specifically to a coating of polylysine on culture dishes; this adhesion can be modified by various treatments to cell membranes, such that an investigation of the surface moieties responsible for the adhesion is being performed. (3) Cultures prepared from cerebellum cells of 16 day fetal rats were found to maintain their large neurons for long periods without high (K ion) in the culture medium. Such cultures are being employed for developmental studies of the electrical and biochemical properties of the cells. (4) Cultures of pineal cells were established and studied extensively for morphologic and biochemical characteristics. These cultures mimic normal pineal glands in most regards, but differ in some aspects of morphology and biochemistry.